Spray it on almost in the same way Asathecomic does, with the exception that i don’t spray it on my hands and rub my head, i spray it behind the earlobe’s and than use the inner wrist to spread it there.
You don’t want it on your hands!

You’re also right that local adjectives for a city are usually formed with the suffix “-er”, for example Hamburger for something coming from Hamburg, Berliner for something coming from Berlin etc. Following this rule, “water from Cologne” would be “Kölner Wasser” in German.

But eau de cologne is an exception. In this case, the suffix for the local adjective is “-isch” (which is usually used for countries, like the English suffix “-ish” in “English”, “Spanish” etc). So, eau de cologne is “Kölnisch Wasser” in German. It is sold as “Kölnisch Wasser” in the German speaking countries for several centuries anyway.